Apparatus and methods for sidewall percussion coring using a voltage activated igniter

ABSTRACT

An apparatus and methods for sidewall percussion coring service are disclosed. In some embodiments, the side-wall percussion coring tool includes a voltage activated igniter, explosive material, and a core barrel in communication with the explosive material, wherein activation of the igniter causes detonation of the explosive material to propel the core barrel from tool. Some method embodiments for performing sidewall percussion coring service using the disclosed sidewall percussion coring tool include positioning the tool within a wellbore, activating the voltage activated igniter housed within the tool, detonating the explosive material within the tool with the voltage activated igniter, propelling a core barrel from the tool into the surrounding formation by detonation of the explosive material, retrieving the core barrel from the formation, and removing the tool from the wellbore.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority toPCT/US2006/061251 filed 27 Nov. 2006, which is incorporated herein byreference in its entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

In a drilled well, representative samples of rock are often cored fromthe formation using a hollow coring bit and transported to the surfacefor analysis. To collect these core samples, a number of coring methodsmay be used, including conventional coring and sidewall coring. Withconventional coring, the drillstring is first removed from the wellboreand then a rotary coring bit with a hollow interior for receiving thecut core sample is run into the well on the end of the drillstring.Sidewall coring, on the other hand, involves removing the core samplefrom the bore wall of the drilled well. There are generally two types ofsidewall coring tools, rotary and percussion. Rotary coring is performedby forcing an open, exposed end of a hollow cylindrical coring bitagainst the wall of the bore hole and rotating the coring bit againstthe formation. Percussion coring uses cup-shaped percussion coring bits,called barrels, that are propelled against the wall of the bore holewith sufficient force to cause the barrel to forcefully enter the rockwall such that a core sample is obtained within the open end of thebarrel. The barrels are then pulled from the bore wall usingconnections, such as cables, wires, or cords, between the coring tooland the barrel as the coring tool is moved away from the lodged coringbit. The coring tool and attached barrels are finally returned to thesurface where core samples are recovered from the barrels for analysis

In a typical percussion coring tool, an explosive device is used topropel the barrel from the tool into the surrounding formation. Thisexplosive device is usually electrically fired, meaning an electricalcurrent is used to initiate the explosion. Because these explosivedevices are electrically initiated, they may be inadvertently initiatedby stray voltage, static charge buildup, and radio frequency energy. Inpopulated areas, sources of radio frequency may include CB radio,cellular telephones, radar, microwaves used for special communicationand heat generation, conventional radio signals, power lines, high poweramplifiers, high frequency electrical transformers, coaxial cables, etc.With respect to locations offshore, another source of radio frequency ispowerful land-based transmitters used to communicate with equipmentlocated on offshore platforms. Given the vast number of stray radiofrequency sources, shutting these sources down temporarily so thatsidewall percussion coring may be performed is impractical, if notimpossible, particularly in congested areas near land-based oil and gasfields.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of the present invention, reference willnow be made to the accompanying drawings, wherein:

FIG. 1 is cross-sectional view of one embodiment of a voltage activatedigniter;

FIG. 2 is a schematic illustration of the electrical circuit for thevoltage activated igniter depicted in FIG. 1;

FIG. 3 is a cross-sectional view of one embodiment of a core guncomprising a voltage activated igniter;

FIG. 4 is an end view of the core gun depicted in FIG. 3; and

FIGS. 5A to 5D depict a typical sequence for removing a core sampleusing a sidewall percussion coring tool comprising the voltage activatedigniter depicted in FIG. 1.

DETAILED DESCRIPTION

Various embodiments of a sidewall percussion coring tool comprising avoltage activated igniter and its method of use will now be describedwith reference to the accompanying drawings. In the drawings anddescription that follow, like parts are marked throughout thespecification and drawings with the same reference numerals,respectively. The drawing figures are not necessarily to scale. Certainfeatures of the invention may be shown exaggerated in scale or insomewhat schematic form, and some details of conventional elements maynot be shown in the interest of clarity and conciseness.

Embodiments of the sidewall percussion coring tool and methods disclosedherein may be used in any type of application, operation, or processwhere it is desired to perform sidewall percussion coring service.Moreover, the tool and its methods of use are susceptible to embodimentsof different forms. Specific embodiments are described in detail and areshown in the drawings, with the understanding that the presentdisclosure is to be considered an exemplification of the principles ofthe invention, and is not intended to limit the invention to thatillustrated and described herein. It is to be fully recognized that thedifferent teachings of the embodiments discussed below may be employedseparately or in any suitable combination to produce desired results.Any use of any form of the terms “connect”, “engage”, “couple”,“attach”, or any other term describing an interaction between elementsis not meant to limit the interaction to direct interaction between theelements unless specifically noted and may also include indirectinteraction between the elements described. The various characteristicsmentioned above, as well as other features and characteristics describedin more detail below, will be readily apparent to those skilled in theart upon reading the following detailed description of the embodiments,and by referring to the accompanying drawings.

FIG. 1 illustrates a cross-sectional view of a representative voltageactivated igniter 100 comprising a housing 105 having a bore 110therethrough, an explosive charge 115, a bleeder resistor 120, acapacitor 125, a semiconductor bridge (SCB) 130, and a spark gap 135 forprotecting the igniter 100 against accidental initiation. The SCB 130and the spark gap 135 are connected by a pair of electrically conductivewires 140, 145 to a means (not shown) for introducing an electricalcharge into the SCB 130 The electrical charge is introduced to the SCB130 by applying positive DC voltage across the leads 150 using anysuitable means in the art, such as but not limited to, electrical wiringrun downhole from the surface or a battery. The housing 105 at one endis sealed with a seal cap 155 and, surrounding that, a pressure sealboot 160. In other embodiments, the seal cap 155 may be replaced with aradio frequency attenuator 163. At the opposite end of the igniter 100,a venting tube 160 is inserted into and extends from the explosivecharge 115. An end seal cap 165 acts as a barrier between the explosivecharge 115 and the surrounding environment.

The housing 105 of the voltage activated igniter 100 includes a bore 110therethrough, the diameter being sufficient to permit inclusion of anSCB 130 within the bore 110. The thickness of the housing wall varies,typically ranging from 0.075″ to 0.125 inches thick. The housing 105 iscomprised of substantially any material of high impedance, such as, forexample, aluminum, steel, stainless steel, brass, and rigid plastics.Regardless of the housing 105 material, it must be suitable for hightemperature applications, i e., temperatures up to 400 degreesFahrenheit or above.

The explosive charge 115 may be introduced into the housing 105 as apowder and thereafter compressed by application of, for example, a ramto the explosive 115 at the end 170 of the housing 105. The explosivecharge 115 comprises any suitable explosive material known in the art,such as but not limited to, granular cyclotetramethylene tetranitramine(HMX), hexanitrostilbene (HNS), bis(picrylamino) trinitropyridine (PYX),trinitrotrimethylenetriamine (RDX) and mixtures thereof. The end 170 ofthe housing 10 is sealed by a thin metal or plastic disk that is pressedinto place or by a thin layer of epoxy to provide a seal 165 on theexposed end of the explosive 115 in the bore 110 of igniter 100.

The SCB 130 is positioned within the housing 105 such that it will be incontact with or at least close proximity to the explosive charge 115.Preferably, the SCB 130 is positioned such that it will be in contactwith the surface of the explosive charge 115 exposed in the bore 110.The SCB 130 may be any suitable, commercially available semiconductorbridge in a size capable of insertion within the housing 105. SuitableSCBs are available from, for example, Thiokol Corporation, Elkton, Md.and SCB Technologies, Inc., Albuquerque, N. Mex. The SCB 130 may beactivated by any suitable electrical charge, including but not limitedto, an electrical charge of approximately 173 volts at an amperage ofapproximately 0.010 amps. It is to be understood, however, that otherSCBs suitable for initiating the deflagration reaction with theexplosive charge 115 in the igniter 100 may be used.

The SCB 130 is connected by an electrically conductive wire 175 to aspark gap 135. The spark gap 135 protects the igniter 100 againstaccidental initiation by an electrostatic discharge, stray voltage,radio frequency energy, or other unintended sources of electricalcurrent. The spark gap 135 has a voltage threshold, for example, 150 to158 volts, before passage of an electrical charge to the SCB 130 occurs.This prevents accidental initiation by unintended electrical chargesbelow the threshold. Spark gaps 135 are available with various ratings,and igniters 100 may be prepared using different spark gaps 135 topermit controlled initiation of individual or multiple explosive chargesin response to different electrical charges transmitted from anelectrical source. Suitable spark gaps 135 are available from, forexample, Reynolds Industries, Okyia, and Lumex Opto.

The SCB 130 and spark gap 135 are provided with electrically conductivewires 140, 145 that provide an electrical connection that extendsoutside the housing 105. At the connection end 173 of the igniter 100,the housing 105 may be sealed with plastic resins or similar materials155 that bond to the housing 105 to seal the various components withinthe housing 105. The electrically conductive wires 140, 145 pass throughthe seal cap 155, leaving the leads 150 exposed for application of anelectrical charge. Alternatively, the housing 105 may be sealed byinsertion of a radio frequency attenuator 163, in lieu of the seal cap155, having passageways therethrough to allow the wires 140, 145 toextend from the housing 105. A radio frequency attenuator 163 may reducethe strength of any radio signal present to a level whereby the signalis incapable of accidental initiation of the igniter 100. Suitable radiofrequency attenuators 163 include the MN 68 ferrite device availablefrom Attenuation Technologies, La Plata, Md.

FIG. 2 depicts an electrical circuit for the voltage activated igniter100 comprising the spark gap 135 connected to the SCB 130 by theelectrically conductive wire 175, the capacitor 125, the bleederresistor 120, and the explosive charge 115. The explosive charge 115includes a pyrotechnic 180 and a secondary explosive 185 in contact withthe SCB 130 The capacitor 125 is utilized to store electrical energysufficient to pass through the spark gap 135 and initiate the SCB 130.The bleeder resistor 120 is used to slowly drain the capacitor 125 inthe event the capacitor 125 is partially charged during an interruptedfiring of the igniter 100 Typically, the capacitor 125 is selected toprovide a capacitance of 3.5 mF, while the bleeder resistor 120 providesa 10,000 to 20,000 ohm resistance. Although FIG. 2 illustrates a singlecapacitor 125 and a single resistor 120, one skilled in the art mayreadily appreciate that multiple capacitors of varied capacitancesand/or multiple resistors of varied resistances may be employed toperform these same functions. Moreover, FIGS. 1 and 2 depictillustrations for only one embodiment of a voltage activated igniter.One skilled in the art may readily appreciate that various othercombinations of the disclosed components, e.g. explosive materials,SCBs, and spark gaps, may be utilized to produce the same result, namelya voltage activated igniter that is immune to stray voltage, staticdischarge buildup, and radio frequency energy.

FIGS. 3 and 4 depict cross-sectional and end views, respectively, of asidewall percussion coring tool 200 that utilizes at least one voltageactivated igniter 100 to propel at least one barrel 215 into thesurrounding formation. In some embodiments, including those depicted byFIGS. 3 and 4, the sidewall percussion coring tool 200 is a core gun.The tool 200 utilizes one or more voltage activated igniters 100 toignite one or more quantities of core load explosive 210. Once ignited,the core load explosive 210 detonates, propelling the core barrel 215into the surrounding formation. The at least one voltage activatedigniter 100 is positioned inside cavity 190 within the tool body 195.Leads 150 extend from the outer end of the igniter 100 and may beattached to electrical wiring (not shown) used to apply an electricalcharge to the igniter 100. The connector end 173 of the igniter 100,including the leads 150 and any attached electrical wiring, is sealed byan outer seal 205.

The core barrel 215, which will be propelled into the surroundingformation to collect a core sample, is seated on the core explosive load210 The core barrel 215 includes the barrel shaft 220 through which aslot 225 passes, a seal plug 230, and a seal plug retainer pin 235. Acore barrel retainer cable 240 passes through slot 225 of the barrelshaft 220. Each end of the core barrel retainer cable 240 is wrappedmultiple times around and attached to a cable retainer pin 245, which issecurely fastened to the tool body 195. The seal plug 230 provides ameans of sealing the cable 240 within slot 225 at the base of the barrelshaft 220, while the seal plug retainer pin 235 locks the seal plug 230to the barrel shaft 220. When the core load explosive 210 detonates, thecore barrel 215 is propelled into the formation while remaining tetheredto the tool body 195 by the core barrel retainer cable 240 and the cableretainer pins 245.

FIGS. 5A through 5D schematically depict one embodiment of a sequence ofoperations wherein the sidewall percussion coring tool 200, comprisingmultiple voltage activated igniters 100, is used to collect coresamples. FIG. 5A depicts one representative sidewall percussion coringservice environment comprising a coiled tubing system 300 on the surface305 and one embodiment of a sidewall percussion coring tool 200 beinglowered into a wellbore 310 on coiled tubing 315. The coiled tubingsystem 300 includes a power supply 320, a surface processor 325, and acoiled tubing spool 330. An injector head unit 335 feeds and directs thecoiled tubing 315 from the spool 330 into the wellbore 310. Althoughthis figure depicts the use of coiled tubing 315 to lower the sidewallpercussion coring tool 200 within the wellbore 310, one skilled in theart may readily appreciate that any similar means, for example,wireline, may be used.

FIG. 5B depicts the sidewall percussion coring tool 200, shown in FIG.5A, at the desired position in the wellbore 310 after run-in iscomplete. In this position, the igniters 100 are activated to propel thecore barrels 215 into the surrounding formation 340, wherein eachigniter 100 ignites the explosive charge 115 contained within it andsubsequently detonates the core load explosive 210 in contact with itvia a venting tube 160 to propel a single core barrel 215.

Firing of each igniter 100 is accomplished by applying positive DCvoltage across its leads 150. In some embodiments, the DC voltage sourcemay be electrical wiring run from the surface 305 into the wellbore 310along with and attached to the tool 200. In other embodiments, the DCvoltage source may be a battery(s) attached to or housed within the tool200. As the positive DC voltage is applied to the leads 150, thecapacitor 125 charges until a threshold level is reached, for example,between 130 and 160 volts, at which point the fixed voltage gap breaksdown. Upon gap discharge, current flows through the SCB 130, causing itto vaporize. Vaporization of the SCB 130 generates plasma gases thatignite the pyrotechnic 180. The burning pyrotechnic 180, in turn, causesa deflagration reaction to begin in the secondary explosive 185. Hotgases resulting from burning of the pyrotechnic 180 and the secondaryexplosive 185 of the explosive charge 115 pass through the venting tube160 to ignite and subsequently detonate the core load explosive 210.Upon detonation of the core load explosive 210, the core barrel 215 ispropelled into the formation 340. As shown in FIG. 5C, a single corebarrel 215 is depicted as having been propelled into the formation 340.One skilled in the art may readily appreciate that a single, multiple,or all core barrels 215 housed within the sidewall percussion coringtool 200 may be deployed into the formation 340 in the same fashion.

As depicted in FIG. 5D, the sidewall percussion coring tool 200 andattached core barrels 215 may be removed from the wellbore 310 byretracting the coiled tubing 315. As the coiled tubing 315 is retractedand the tool 200 is pulled towards the surface 305, the core barrelretainer cable 240 remains securely fastened both to the core barrel 215and the tool 200, thereby pulling the core barrel 215 from the formation340 wall. Once extracted from the formation 340, each core barrel 215contains a core sample of the formation 340, which may retrieved fromthe core barrel 215 for analysis after the tool 200 reaches the surface305.

While various embodiments of and methods of using a sidewall percussioncoring tool comprising at least one voltage activated igniter have beenshown and described herein, modifications may be made by one skilled inthe art without departing from the spirit and the teachings of theinvention. The embodiments described are representative only, and arenot intended to be limiting. Many variations, combinations, andmodifications of the applications disclosed herein are possible and arewithin the scope of the invention. Accordingly, the scope of protectionis not limited by the description set out above, but is defined by theclaims which follow, that scope including all equivalents of the subjectmatter of the claims.

1. A sidewall percussion coring tool including: a tool housing; an explosive material disposed within the tool housing; a voltage activated igniter comprising: an igniter housing that defines an internal volume; a semiconductor bridge disposed within the internal volume; a spark gap disposed within the internal volume and electrically coupled in series to the semiconductor bridge; a capacitor disposed within the internal volume and electrically coupled in parallel with the spark gap and semiconductor bridge; a resistor disposed within the internal volume and electrically coupled in parallel with the capacitor; a pyrotechnic that abuts the semiconductor bridge, the pyrotechnic disposed within the internal volume; an explosive charge that abuts the pyrotechnic, the explosive charge disposed within the internal volume; and a vent tube distinct from the igniter housing, the vent tube fluidly coupling the internal volume to the explosive charge into the explosive material; and a core barrel, the core barrel being propellable out of the housing by the detonation of the explosive material.
 2. The tool of claim 1, wherein the core barrel is attached to the sidewall percussion coring tool by a tether, wire, or cable.
 3. The sidewall percussion coring tool of claim 1 wherein the voltage activated igniter further comprises a pressure seal disposed on a first end of the igniter housing opposite the vent tube.
 4. A method of performing sidewall percussion coring service including: positioning a sidewall percussion coring tool within a wellbore; applying a voltage to a voltage activated igniter housed within the sidewall percussion coring tool; activating the voltage activated igniter when the voltage rises above a threshold voltage, the activating by: conducting current across a spark gap disposed within the voltage activated igniter; vaporizing a semiconductor bridge by the current, the semiconductor bridge within the voltage activated igniter; igniting a pyrotechnic by the semiconductor bridge, the pyrotechnic disposed within the voltage activated igniter; causing deflagration of a first explosive by the pyrotechnic, the explosive within the voltage activated igniter; conducing hot gasses to a second explosive material by way of a tube; detonating a second explosive material within the sidewall percussion coring tool by the hot gasses conducted through the tube of the voltage activated igniter; propelling a core barrel from the sidewall percussion coring tool into the surrounding formation by detonation of the explosive material; retrieving the core barrel from the formation; and removing the sidewall percussion coring tool from the wellbore.
 5. The method of claim 4, wherein the positioning is accomplished using coiled tubing or wireline.
 6. The method of claim 4, wherein the voltage is a positive DC voltage applied using electrical wiring run into the wellbore from the surface or a battery housed within the sidewall percussion coring tool.
 7. The method of claim 5, wherein retrieving the core barrel and removing the sidewall percussion coring tool include retracting the coiled tubing or the wireline from the wellbore.
 8. The method of claim 4, wherein removing the sidewall percussion coring tool causes the retrieving the core barrel by means of a tether, cable or wire attached at one end to the core barrel and at the other end to the sidewall percussion coring tool.
 9. The method of claim 4, further including activating more than one voltage activated igniter in series.
 10. The method of claim 4, further including propelling more than one core barrel from the sidewall percussion coring tool.
 11. The method of claim 4, further including extracting a core sample from the core barrel at the surface.
 12. The method of claim 4, wherein the sidewall percussion coring tool is a core gun. 